This patent application claims priority to Japanese Patent Application No. 2000-366594 dated Dec. 1, 2000 entitled xe2x80x9cGolf Club Shaft.xe2x80x9d
The present invention relates to a golf club shaft with improved feeling that is obtained by improving the uniformity of deflection of the golf club shaft during downswing.
Conventionally, in terms of flexural rigidity (EI) of the shaft, the characteristics of the wood-type golf club are generally expressed as xe2x80x98tip kick point,xe2x80x99 xe2x80x98mid kick point,xe2x80x99 and xe2x80x98butt kick point.xe2x80x99
Specifically, EI is made lower in a particular portion of the conventional golf club shaft than in the remaining portions (or made higher in the remaining portions) to decrease the deflection radius of curvature of the particular portion and to adjust the flex of the shaft during a swing.
The shaft of the xe2x80x98tip kick pointxe2x80x99 type refers to a shaft with a lower EI value near the tip portion of the golf club shaft. The xe2x80x98tip kick pointxe2x80x99 type shaft usually generates a greater launching angle of the ball and is considered to be suitable for beginners. The xe2x80x98butt kick pointxe2x80x99 type shaft refers to a shaft with a lower EI value near the grip side, as compared with the xe2x80x98tip kick pointxe2x80x99 type shaft. The xe2x80x98butt kick pointxe2x80x99 type shaft suppresses launching of the ball and is considered suitable for advanced players. The shaft between the both types is the xe2x80x98mid kick pointxe2x80x99 type shaft.
FIG. 1 is a graph showing the EI values of the conventional golf club shafts. The conventional shafts 1, 2, and 3 are the xe2x80x98butt kick pointxe2x80x99 shaft, the xe2x80x98tip kick pointxe2x80x99 shaft, and the xe2x80x98mid kick pointxe2x80x99 shaft, respectively. The axis of abscissas shows the distance from the tip end in the longitudinal direction. The conventional golf club shafts are generally constructed as shown in the graph.
The xe2x80x98tip kick pointxe2x80x99 shaft (conventional shaft 2) has a long portion with a low EI value at the tip portion. The EI value drastically increases therefrom toward the grip portion. The xe2x80x98butt kick pointxe2x80x99 shaft (conventional shaft 1) has low rate of increase of the EI value from the tip portion to the butt portion, resulting in a low EI value at the butt portion. The xe2x80x98mid kick pointxe2x80x99 shaft (conventional shaft 3) has a higher EI value at the tip and butt portions and a lower EI value at the mid portion. The EI value of the shaft greatly varies according to the kick point.
No specific definition has been established for the EI distribution of the kick points of the golf club shaft. The kick points have been mainly determined by design concepts of respective manufacturers. The performance of the golf club shaft may not be properly evaluated according to the designated kick points. For example, no more definite correlation exists between the launching angle of the hit ball and the EI value at the tip portion versus at other portions. Different players like different kick points, whether they are beginners or advanced players. Thus, the EI distribution liked by a majority of players has not been yet established, in spite of struggling efforts by manufacturers.
It is an object of the present invention to provide a golf club shaft having a shaft""s EI distribution liked by every player by improving the deflection shape of the golf club shaft during a swing.
A golf club shaft comprises a reinforced tip portion including a tip end, a gripping butt portion including a grip end, an intermediate portion between the reinforced tip portion and the gripping butt portion. The flexural rigidity and the distance from the tip end are in substantially direct proportion generally over the entire length of the intermediate portion.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.